CENGRS GEOTECHNICA PVT. LTD. Job No. 214030 Sheet No. 1 INTERIM REPORT ON GEOTECHNICAL INVESTIGATION FOR PROPOSED 66 KV GRID PLOT AT G-7, DWARKA, NEW DELHI. 1.0 INTRODUCTION 1.1 Project Description M/s. BSES Rajdhani Power Ltd. is planning to construct the proposed 66 KV Grid Substation at G-7, Dwarka, New Delhi. We understand that various facilities are planned to be constructed at the site, including EVH staff room, control room, capacitor bank and switchyard. M/s. Cengrs Geotechnica Pvt. Ltd. (Cengrs) has carried out the geotechnical investigation at the proposed site. A layout plan showing the locations of our field investigation for this project is presented on Fig. 1. This interim report presents our preliminary engineering recommendations, based on eight (8) boreholes and one (1) electrical resistivity test completed at project site. Laboratory testing of the soil samples collected from the boreholes is currently in progress. Our final report shall be submitted on completion of the laboratory-testing program. 1.2 Test Locations below: Details of the various tests completed at the project site are tabulated Exploratory Boreholes Structure Borehole UTM Coordinates Designati on Easting Northing Termination Depth, m EVH STAFF ROOM BH-1 702510 3162886 7.90 m CONTROL ROOM BH-2 702521 3162876 10.45 m BH-3 702541 3162866 10.45 m CAPACITOR BANK BH-4 702555 3162877 10.42 m BH-5 702571 3162863 10.45 m SWITCHYARD BH-6 702578 3162876 10.45 m BH-7 702588 3162891 10.38 m BH-8 702595 3162862 10.45 m
CENGRS GEOTECHNICA PVT. LTD. Job No. 214030 Sheet No. 2 Electrical Resistivity Test Structure Test Designation Easting UTM Coordinates Northing SWITCHYARD ERT-1 702575 3162878 A layout plan illustrating the various test locations is presented on Fig.1. The borehole locations were marked on the field using a Global Positioning System (GPS) by our Engineer, and compared with the site layout plan provided to us. A satellite image indicating the site and test locations (as recorded by GPS) is presented on Fig. 2. Reduced levels (RL) at the test locations are not provided to us by the client on site. The depths referred to in this report are with respect to the existing ground levels at the time of our field investigations, unless mentioned otherwise. 2.0 GENERAL SITE CONDITIONS 2.1 Site Stratigraphy Fill material consisting of heterogeneous mixture of sandy silt with gravel is encountered at the borehole locations to about 0.3-0.5 m below EGL. Below this, medium dense to dense sandy silt is encountered to the final explored depth of 10 m. The field SPT values in the silt stratum generally range from 16-40 to about 2 m depth indicating medium dense to dense soil condition. Below this, the field SPT-N values range from 23-53 to about 5 m depth. Below this, the field SPT-N values range from 52 to refusal (N>100) to the final explored depth of 10 m indicating dense to very dense condition. A summary of the borehole profiles (based on our visual assessment) is illustrated on Fig. 3. Field and corrected SPT values are presented on Fig. No s. 4a & 4d, respectively. 2.2 Groundwater Based on our measurements in the boreholes, groundwater was not met to the maximum explored depth of 10 m depth at the time of our field investigation (February, 2014). We expect ground water at this location to be fairly deep. 3.0 INTERPRETATION OF ELECTRICAL RESISTIVITY TEST RESULT One (1) electrical resistivity test has been performed at the specified location as illustrated on Fig. No. 1.
CENGRS GEOTECHNICA PVT. LTD. Job No. 214030 Sheet No. 3 The test results are presented on Fig. No s. 5a & 5b. The apparent resistivity values obtained have been analyzed to generate the polar curve. The polar curve is used to compute the mean resistivity. A mean resistivity value of 12 ohm-m is obtained at ERT-1 location. This value may be used for the design of the electrical grounding system. 4.0 FOUNDATION ANALYSIS AND RECOENDATIONS 4.1 General A suitable foundation for any structure should have an adequate factor of safety against exceeding the bearing capacity of the supporting soils. Also, the vertical movements due to compression of the soils should be within tolerable limits for the structure. We consider that foundations designed in accordance with the recommendations given herein will satisfy these criteria. 4.2 Liquefaction Susceptibility Assessment Liquefaction is defined as the transformation of a granular material from a solid to a liquefied state as a consequence of increased pore-water pressure and reduced effective stress (Marcuson, 1978 1 ). Increased pore pressure may be induced by the tendency of granular materials to compact when subjected to cyclic shear deformation, such as in the event of an earthquake. As per IS: 1893-2002, liquefaction is likely to occur in loose fine sand below water table. Since groundwater is not encountered at the project site to the maximum explored depth of 10 m, we are of the opinion that the soils at the site are not likely to liquefy in the event of an earthquake. According to Fig.1 of IS: 1893 (Part1)-2002 showing seismic zones, the proposed site falls under Zone-IV. The design for seismic forces should be done considering the project in Zone-IV. 4.3 Foundation Type and Depth Open spread foundations, isolated footings or strip footings with interconnecting beams may be used to support the structural loads. We are of the opinion that open foundations may be a suitable foundation scheme to support the structural loads. Preliminary recommendations for open foundations bearing at 1.5-2 m depth below EGL are presented in Section 4.4. 4.4 Preliminary Net Allowable Bearing Pressures The following table presents our suggested values of net allowable bearing pressures bearing at 1.5-2 m depth below EGL: (1) Marcuson, W.F. (III) (1978), Definition of terms related to liquefaction, J. Geotech Engrg. Div,, ASCE, 104(9), 1197-1200.
CENGRS GEOTECHNICA PVT. LTD. Job No. 214030 Sheet No. 4 Foundation Depth, m Suggested Net Allowable Bearing Pressure, T/m 2 Total Settlement =40mm Total Settlement =50mm Suggested Modulus of Subgrade Reaction kn/m 3 1.5 14.0 17.5 3500 2.0 17.6 22.0 4400 The above values include a bearing capacity safety factor of 2.5. The appropriate values of net bearing pressure may be selected as per the permissible settlement criterion. Net bearing pressures for foundations at intermediate depths may be interpolated linearly between the values given above. In order to restrict the influence of adjacent footings on each other, the lateral edge-to-edge spacing between the foundations should at least be equal to "0.8B" where "B" is the width of the larger footing. In case this criterion cannot be satisfied, combined footings or raft foundations ay be provided. 4.5 Definition of Net Bearing Pressure For the purposes of this report, the net allowable bearing pressure should be calculated as the difference between total load on the foundation and the weight of the soil overlying the foundation divided by the effective area of the foundation. The gross bearing pressure is the total pressure at the foundation level including overburden pressure and surcharge load. The following equations may be used q net = [(P s + W f + W s ) / A f ] - S v q gross = q net + S v = (P s + W f + W s ) / A f where: q net = net allowable bearing pressure q gross = gross bearing pressure P s = superimposed static load on foundation W f = weight of foundation W s = weight of soil overlying foundation A f = effective area of foundation S v = overburden pressure at foundation level prior to excavation for foundation. It may please be noted that safe bearing pressures recommended in this report refer to net values. Where filling is done, it should be treated as a surcharge over the foundation.
CENGRS GEOTECHNICA PVT. LTD. Job No. 214030 Sheet No. 5 5.0 FOUNDATION CONSTRUCTION CONSIDERATIONS 5.1 Excavation Temporary open-cut excavation for foundation construction to about 2 m depth may be done using side slope of 1-vertical and 0.3~0.5 horizontal. The excavation slopes should be monitored by the engineer. In case excessive sloughing or caving occurs, the slopes may be flattened further to ensure stability. 5.2 Foundation Level Preparation The area shall be excavated up to the foundation level. All loose soils should be removed and the exposed foundation bearing surface should be compacted properly using rammers / rollers. The surface should then be protected from disturbances due to construction activities so that the foundations may bear on the natural undisturbed ground. We recommend the placement of a 75 to 100 mm thick blinding layer of lean concrete to facilitate placement of reinforcing steel and to protect the soils from disturbance. In case mechanical means like excavators are deployed for excavations, the excavations should be carried out up to 0.5 m above the proposed level. The last 0.5 m depth of excavation should be carried out manually, so that the founding soils are not disturbed / loosened. 5.3 Variability In Sub-surface Condition Subsurface conditions encountered during construction may vary somewhat from the conditions encountered during the site investigation. In case significant variations are encountered during construction, we request to be notified so that our engineers may review the recommendations in this report in light of these variations. 6.0 CLOSURE We appreciate the opportunity to submit this interim report. We wish to emphasize here that the recommendations given in this report are preliminary and subject to change. Laboratory testing of the soil samples collected is currently in progress. Our final report will be submitted upon detailed analysis of all field and laboratory data. In the meantime, please feel free to contact us for any further information. for CENGRS GEOTECHNICA PVT. LTD. (RAVI SUNDARAM) DIRECTOR
CENGRS GEOTECHNICA PVT. LTD. Job.No.: 214030 Fig No.: 1 N BH 1 BH 2 BH 3 BH 4 BH 5 BH 6 BH 7 BH 8 SYMBOL L E G E N D TYPE OF TEST Borehole (BH) Plan of Field Investigation
CENGRS GEOTECHNICA PVT. LTD. Job.No.: 214030 Fig No.: 2 Test No. UTM Coordinates (Zone 43 R) BH 1 702510.00 m E 3162886.00 m N BH 2 702521.00 m E 3162876.00 m N BH 3 702541.00 m E 3162866.00 m N BH 4 702555.00 m E 3162877.00 m N BH 5 702571.00 m E 3162863.00 m N BH 6 702578.00 m E 3162876.00 m N BH 7 702588.00 m E 3162891.00 m N BH 8 702595.00 m E 3162862.00 m N ERT 1 702575.00 m E 3162878.00 m N N Satellite image taken from Google Earth Test Locations marked as per GPS coordinates taken on site using hand-held Garmin device Accuracy of hand-held GPS device generally ranges from 4-6m, and varies depending on the availability of satellite connection at the site Satellite Image of Site and Test Locations
CENGRS GEOTECHNICA PVT. LTD. Job.No.: 214030 Fig No.: 3 BH-1 BH-2 BH-3 BH-4 BH-5 BH-6 BH-7 BH-8 0 0.5 0.5 0.3 0.3 0.3 0.3 0.3 0.3 2 45 40 18 55 38 16 32 24 77 47 25 44 40 23 47 25 4 102/23cm 102/26cm 45 49 74 40 53 28 DEPTH, m 6 101/20cm 95 84 49 58 69 89 58 8 7.90m 101/25cm 76 59 52 65 71 90 33 10 EVH Staff Room 101/25cm 79 102/19cm 69 101/26cm 102/27cm 101/27cm 96 103/20cm 83 102/27cm 101/23cm 77 73 10.45m 10.45m 10.42m 10.45m 10.45m 10.38m 10.45m 12 Control Room Capacitor Bank Switchyard SYMBOL L E G E N D DESCRIPTION FILL Sandy silt (CL) Note : Soil classification is preliminary and visual assessment Summary of Borehole Profiles
CENGRS GEOTECHNICA PVT. LTD. Job No. 214030 Fig No. 4a Field SPT Value (N) 0 0 10 20 30 40 50 60 70 80 90 100 1 2 3 Depth, m 4 5 6 102/23cm 102/26cm 7 8 9 101/25cm 101/26cm 101/27cm 10 11 L E G E N D Symbol BH.No. 1 2 3 4 Reduced Level,m Standard Penetration Test Results (Field Values)
CENGRS GEOTECHNICA PVT. LTD. Job No. 214030 Fig No. 4b 0 Corrected SPT Value (N") 0 10 20 30 40 50 60 70 80 90 100 1 2 3 4 102/23cm 102/26cm Depth, m 5 6 7 8 9 10 101/25cm 101/26cm 11 L E G E N D Symbol BH.No. 1 2 3 4 Reduced Level,m Standard Penetration Test Results (Corrected Values)
CENGRS GEOTECHNICA PVT. LTD. Job No. 214030 Fig No. 4c Field SPT Value (N) 0 0 10 20 30 40 50 60 70 80 90 100 1 2 3 4 5 Depth, m 6 7 8 9 103/20cm 102/27cm 101/27cm 10 11 L E G E N D Symbol BH.No. 5 6 7 8 Reduced Level,m Standard Penetration Test Results (Field Values)
CENGRS GEOTECHNICA PVT. LTD. Job No. 214030 Fig No. 4d 0 Corrected SPT Value (N") 0 10 20 30 40 50 60 70 80 90 100 1 2 3 4 Depth, m 5 6 7 8 9 103/20cm 10 102/27cm 11 L E G E N D Symbol BH.No. 5 6 7 8 Reduced Level,m Standard Penetration Test Results (Corrected Values)
CENGRS GEOTECHNICA PVT. LTD. Job No.: 214030 Fig No: 5a Electrical Resisitivity Test No.: ERT-1 IS : 3043-1987 Strureture UTM Co-ordinate : : Switchyard 702575.00 me, 3162878.00 mn 100 Apparent Resistivity,Ohm-m 10 E-W SE-NW E-W (Reverse) SE-NW (Reverse) N-S N-S (Reverse) SW-NE SW-NE (Reverse) 1 0 2 4 6 8 10 12 14 16 Electrode Spacing, m Electrode Spacing, m 1.0 2.0 3.0 5.0 7.0 10.0 12.0 15.0 Mean Resistivity E-W E-W (Revers SE-NW e) Apparent Resistivity, Ohm-m SE-NW (Revers e) N-S N-S (Reverse) SW-NE SW-NE (Reverse) 10.4 10.4 14.4 14.3 11.2 11.4 13.8 14.2 18.8 18.5 20.2 20.5 20.5 20.2 19.1 19.2 12.1 12.1 15.3 15.8 10.7 11.1 10.7 11.1 15.7 16.0 20.1 19.8 15.1 14.8 14.5 15.1 8.4 9.2 15.8 16.3 7.0 6.6 9.7 10.1 12.6 12.6 18.2 18.8 8.2 8.2 11.3 10.7 11.3 12.1 12.8 13.6 8.3 9.0 9.0 9.0 9.4 10.4 12.3 11.3 9.4 10.4 10.4 11.3 12 13 14 14 13 13 12 13 Mean Resistivity Value, ohm-m : 12 Apparent Resistivity Values Electrical Resistivity Test
CENGRS GEOTECHNICA PVT. LTD. Job No.: 214030 Fig No.: 5b Electrical Resisitivity Test No.: ERT-1 IS : 3043-1987 Strureture UTM Co-ordinate : Switchyard : 702575.00 me, 3162878.00 mn NW 25 N NE 20 15 0.0, 12.5-9.7, 9.7 10 8.9, 8.9 5 W -12.6, 0.0 0 12.3, 0.0-25 -20-15 -10-5 0 5 10 15 20 25-5 E -8.7, -8.7-10 9.7, -9.7-15 0.0, -12.8-20 SW -25 S SE Total Area of Polygon = Radius of Equivalent Circle=Mean Resistivity = 466 12 ohm-m Polar Resistivity Curves Electrical Resistivity Test